The objective of this study has been to evaluate a method for the detection of the tumor-associated antigen, CEA (carcinoembryonic antigen), as an adjunct to standard cytologic examinatons of body fluids in cancer screening. The goal has been to use the CEA-immunoperoxidase technique to re-examine body fluids containing "suspicious" and "atypical" cells for a more accurate marker for malignancy. The three-year goal was to examine approximately 5,300 specimens collected routinely in our cytology laboratoies. During the past 10 months 1,346 immunohistologic preparations were stained for CEA with appropriate non-immune serum controls. The results are as follows (source, followed by number of CEA-positive preparations, number of CEA-negative preparations, and number of negative controls): pleural - 11, 169, 180; bronchial - 19, 141, 160; sputum - 24, 191, 215; peritoneal -8, 82, 90; urine - 22, 6, 28. Among the negative controls (non-immune serum substituted for anti-CEA) only granulocytes and histiocytes containing native peroxidase showed a positive reaction and these were readily distinguished from epithelial cells. We are currently beginning to review the cytologic diagnoses and clinical data of all patients studied.